1. Field of the Invention
The present invention relates to a semiconductor-containing glass and the method of producing the same, and in particular, relates to a semiconductor-containing glass produced by making microcrystals of a compound semiconductor be contained in a glass matrix produced by a sol-gel technique, and the method of producing the same. The semiconductor-containing glass according to the present invention is utilized as a glass material having a large non-linear optical effect used in the field of optical information such as light switches, light wavelength converter elements, etc.
2. Prior Art
The semiconductor-containing glass is given attention as a non-linear optical material usable for light switches, light wavelength converter elements, etc. because it has optical bi-stability, a light buffer time of the order of ps (picosecond) a quantum size effect, etc. A multicomponent glass containing about 1% of CdS microcrystals or containing about 1% of CdS.sub.x Se.sub.(1-x) microcrystals is generally known as such semiconductor microcrystal-containing glass (hereinafter also called "a semiconductor-containing glass") and available as filter glass. This type semiconductor-containing glass is produced by heating raw materials which will be a glass matrix and a compound semiconductor respectively to prepare a glass melt and then quenching and re-heating the glass.
It can be, however, hardly said that the conventional semiconductor-containing glass produced by such a melting method is useful as a non-linear optical material, from the following points of view. Because volatilization of raw semiconductor materials occurs when a glass melt is prepared, the semiconductor microcrystal concentration in the glass is small. Because the semiconductor microcrystal grows disorderly in the re-heating treatment after quenching, the semiconductor microcrystals are uneven in size. It is difficult to make a thin film. The kinds of the compound semiconductors allowed to be contained in the glass are limited.
Therefore, various attempts to produce a semiconductor-containing glass by using novel techniques of producing amorphous materials (e.g. a sol-gel technique, a CVD technique, sputtering technique, a simultaneous evaporation technique, a lithographic technique, and a method using a porous glass) have been made for the purposes of increase in the semiconductor microcrystal concentration in the glass, uniformization of the size of the semiconductor microcrystal, formation of the glass in the form of a thin film, etc. At the same time, various attempts to produce various semiconductor-containing silica glasses have been made in order to obtain various kinds of semiconductor-containing glasses having the non-linear optical characteristics and various optical characteristics. With the attempts, other semiconductor-containing silica glasses containing microcrystals or fine particles of CuS, CuCl, Au, Si, Mn.sub.2 O.sub.3, In/GaAs, GaAs, InP, CdSe, ZnSe, CdTe, CdS.sub.x Se.sub.(1-x-y) Te.sub.y, etc. as a semiconductor than the semiconductor-containing silica glass containing CdS microcrystals or CdS.sub.x Se.sub.(1-x) microcrystals has been prepared. Further, attempts have been made to obtain various kinds of semiconductor-containing multicomponent glass.
When producing the semiconductor-containing glass containing compound-semiconductor microcrystals among those various kinds of semiconductor-containing glasses, it is preferable that a sol-gel technique is used. This is because the increase in the compound semiconductor microcrystal concentration is relatively easy; uniformity of the size of the semiconductor microcrystal is relatively high; the degree of freedom in the shape of the finally produced glass is relatively high; the restriction in the kind of the semiconductor allowed to be contained in the glass is loose; and the like. For example, each of the following methods i to vi is known as a method for producing a semiconductor-containing glass containing compound-semiconductor microcrystals, on the basis of the sol-gel technique.
i. A method comprising the steps of: preparing any one of a sol solution in which both a metallic element and a non-metallic element are contained as raw materials for a compound semiconductor, a sol solution in which a compound semiconductor is dissolved, and a sol solution in which a compound to be changed to a semiconductor by reduction is dissolved; preparing a dry gel by gelating the sol solution and then drying it; and producing a semiconductor-containing glass by applying preliminary heat treatment to the dry gel to precipitate compound semiconductor microcrystals before vitrification and then applying heat treatment thereto again or by precipitating compound semiconductor microcrystals by heat treatment for vitrification of the dry gel.
ii. A method comprising the steps of: preparing a sol solution containing one of a metallic element and a non-metallic element as a raw material for a compound semiconductor; preparing a wet gel from the sol solution; impregnating the wet gel with a solution containing the other one of the metallic element and the non-metallic element as a constituent member of the compound semiconductor and then preparing a dry gel; and producing a semiconductor-containing glass by applying preliminary heat treatment to the dry gel to precipitate compound semiconducor microcrystals before vitrification and then applying heat treatment thereto again or by precipitating compound semiconductor microcrystals by heat treatment for vitrification of the dry gel.
iii. A method comprising the steps of: preparing a sol solution containing one of a metallic element and a non-metallic element as a raw material for a compound semiconductor; preparing a dry gel by gelating the sol solution and drying it; impregnating the dry gel with a solution containing the other one of the metallic element and the non-metallic element as a constituent member of the compound semiconductor and then preparing a dry gel; and producing a semiconductor-containing glass by applying preliminary treatment to the dry gel to precipitate compound semiconductor microcrystals before vitrification and then applying heat treatment thereto again or by precipitating compound semiconductor microcrystals by heat treatment for vitrification of the dry gel.
iv. A method comprising the steps of: preparing a wet gel by gelating a sol solution corresponding to the composition of a glass matrix; preparing a dry gel after impregnating the wet gel with any one of a sol solution in which both a metallic element and a non-metallic element are contained as raw materials for a compound semiconductor, a sol solution in which a compound semiconductor is dissolved, and a sol solution in which a compound to be changed to a semiconductor by reduction is dissolved; and producing a semiconductor-containing glass by applying preliminary heat treatment to the dry gel to precipitate compound semiconductor microcrystals before vitrification and then applying heat treatment thereto again or by precipitating compound semiconductor microcrystals by heat treatment for vitrification of the dry gel.
v. A method comprising the steps of: preparing a dry gel by gelating a sol solution corresponding to the composition of a glass matrix; impregnating the dry gel with any one of a sol solution in which both a metallic element and a non-metallic element are contained as raw materials for a compound semiconductor, a sol solution in which a compound semiconductor is dissolved, and a sol solution in which a compound to be changed to a semiconductor by reduction is dissolved; and producing a semiconductor-containing glass by applying preliminary heat treatment to the dry gel to precipitate compound semiconductor microcrystals before vitrification and then applying heat treatment thereto again or by precipitating compound semiconductor microcrystals by heat treatment for vitrification of the dry gel.
vi. A method disclosed in Japanese Patent Unexamined Publication No. Hei-1-183438.
Here, the method disclosed in the Japanese Patent Unexamined Publication No. Hei-1-183438 is a method for doping a dry gel with a compound semiconductor having a small particle size and having a uniform particle size distribution by the following techniques:
(a) Immersing a dry gel (which has been described as "porous glass" in the above Japanese Patent Unexamined Publication but it is apparent that the "porous glass" described therein is equivalent to dry gel considering the heat treatment condition described in the above Japanese Patent Unexamined Publication) in a dispersion of hydrosol or organosol of a compound semiconductor, drying and heating it.
(b) Making a metal element as a raw material for a compound semiconductor be contained in a sol solution to prepare a dry gel, and then making the dry gel react with a hydrogen sulfide gas at a room temperature for a long time.
The present invention has been attained in the existing circumstances of a semiconductor-containing glass.
A first object of the present invention is to provide a novel semiconductor-containing glass having, as a glass matrix, multicomponent glass produced by a sol-gel technique.
A second object of the present invention is to provide a novel semiconductor-containing glass having, as a glass matrix, silica glass produced by a sol-gel technique.
A third object of the present invention is to provide a method for solving the problems in the conventional semiconductor-containing glass producing methods based on a sol-gel technique, that is, to provide a method for solving the problems in the aforementioned conventional methods (i to v) in which a dry gel has (a) both a metal element and a non-metal element as raw compound semiconductor materials or (b) a compound semiconductor contained therein at the stage of dry gel, and in the aforementioned conventional method (vi) in which a dry gel is doped with a compound semiconductor at the stage of the dry gel. As described above, in the conventional methods, the heat treatment of the dry gel is necessary for producing a semiconductor-containing glass having a practically sufficient mechanical strength. Because oxidization or volatilization of the metal element and/or the non-metal element occurs in the heat treatment in the conventional methods, or because oxidization, volatilization or decomposition of the compound semiconductor contained in the dry gel or as a dopant in the dry gel occurs in the heat treatment, the semiconductor allowed to be contained in the finally produced semiconductor-containing glass is severely restricted as to the kind and the quantity thereof. The third object of the present invention is therefore to provide a method of producing a semiconductor-containing glass in which: lowering of the compound semiconductor content caused by the heat treatment for forming glass can be suppressed when a semiconductor-containing glass having compound semiconductor microcrystals dispersively precipitated is produced by a sol-gel technique; the size of the compound semiconductor microcrystals can be controlled when a semiconductor-containing glass having compound semiconductor microcrystals dispersively precipitated is produced by the sol-gel technique; and the method can be applied to various kinds of compound semiconductors.